Diagram showing how to measure the length and circumference of an erect human penis

The most accurate measurement of human penis size can be derived from several readings at different times since there is natural minor variability in size depending upon arousal level, time of day, room temperature, frequency of sexual activity, and reliability of measurement. When compared to other primates, including large examples such as the gorilla, the human penis is thickest, both in absolute terms and relative to the rest of the body.

Measurements vary, with studies that rely on self-measurement reporting a significantly higher average than those with a health professional measuring. As of 2015[update], a systematic review of the best research to date on the topic has concluded that the mean length of an erect human penis is approximately 13.12 ± 1.66 cm (5.17 ± 0.65 in).[1] Flaccid penis length is generally a poor predictor of erect length.

Most human penis growth occurs between infancy and the age of five, and between about one year after the onset of puberty and, at latest, approximately 17 years of age.[2]

A statistically significant correlation between penis size and the size of other body parts has not been found in research. Some environmental factors in addition to genetics, such as the presence of endocrine disruptors, can affect penis growth. An adult penis with an erect length of less than 7 cm (2.8 in), but otherwise formed normally, is referred to in medicine as a micropenis.

Penis size is positively correlated with increasing testosterone levels during puberty.[3] However, after puberty, administration of testosterone is not capable of affecting penis size, and androgen deficiency in adult men only results in a small decrease in size.[3]Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are also involved in penis size, with deficiency (such as that observed in growth hormone deficiency or Laron syndrome) at critical developmental stages having the potential to result in micropenis.[4]

History

Fresco of Priapus from Pompeii, depicted weighing his large erect penis against a bag of gold. Ancient Romans admired the large penis of Priapus.[5]

Perceptions of penis size are culture-specific. In Ancient Greece and in Renaissance art, a small penis which had not been circumcised was perceived as desirable in a man, whereas a large or circumcised penis was considered comical or grotesque. Ancient Rome may have had a contrary view, and a larger penis size was preferred in medieval Arabic literature.[citation needed] Males may quite easily underestimate the size of their own penis relative to that of others, and many men who believe that their penis is of inadequate size have average-sized penises. The perception of having a large penis is often linked to higher self-esteem.[6] Fears of shrinking of the penis in folklore have led to a type of mass hysteria called penis panic, though the penis legitimately can shrink in size due to scar tissue formation in the penis from a medical condition called Peyronie's disease.[7][8] Marketers of penis enlargement products exploit fears of inadequacy, but there is no consensus in the scientific community of any non-surgical technique that permanently increases either the thickness or length of the erect penis that already falls into the normal range.

Studies

Distribution of penis sizes by circumference. Erected penises (green) are 81% between 10 and 13 cm in circumference.[1]

While results vary slightly across reputable studies, the consensus is that the mean human penis is in the range 12.9–15 cm (5.1–5.9 in) in length with a 95% confidence interval of (10.7 cm, 19.1 cm) or, equivalently (4.23 in, 7.53 in) — that is, it is 95% certain that the true mean is at least 10.7 cm but not more than 19.1 cm.[9][10][11]

A 2015 systematic review published by Veale et al. of medical research on the topic over the previous 30 years published in BJU International showed similar results, giving mean flaccid, stretched non-erect, and erect lengths of 9.16 cm, 13.24 cm, and 13.2 cm respectively, and mean flaccid and erect circumferences of 9.31 cm and 11.66 cm respectively. Erect lengths in the included studies were measured by pushing the pre-pubic fat pad to the bone, and flaccid or erect girth (circumference) was measured at the base or mid-shaft of the penis.[1]

Length

Flaccid

One study found the mean flaccid penis length to be 3.5 inches (8.9 cm) (measured by staff).[9] A review of several studies found average flaccid length to be 9–10 cm (3.5–3.9 in).[12] Length of the flaccid penis does not necessarily correspond to length of the erect penis; some smaller flaccid penises grow much longer, while some larger flaccid penises grow comparatively less.[13]

The penis and scrotum can contract involuntarily in reaction to cold temperatures or nervousness, referred to by the slang term "shrinkage", due to action by the cremaster muscle. The same phenomenon affects cyclist and exercise bike users, with prolonged pressure on the perineum from the bicycle saddle and the straining of the exercise causing the penis and scrotum to contract involuntarily. An incorrect saddle may ultimately cause erectile dysfunction (see crotch pressure for more information).

Stretched

Neither age nor size of the flaccid penis accurately predicted erectile length. Stretched length has correlated with erect length in some cases.[9] However studies have also shown drastic differences between stretched and erect length.[14]

Erect

Scientific studies have been performed on the erect length of the adult penis. Studies that have relied on self-measurement, including those from Internet surveys, consistently reported a higher average length than those that used medical or scientific methods to obtain measurements.[11][15]

The following staff-measured studies are composed of different subgroups of the human population (i.e., specific age range and/or race; selection of those with sexual medical concerns or self-selection) that could cause a sample bias.[15][16]

In a study of 80 healthy males published in the September 1996 Journal of Urology an average erect penis length of 12.9 cm (5.1 in) was measured.[9] The purpose of the study was to "provide guidelines of penile length and circumference to assist in counseling patients considering penile augmentation." Erection was pharmacologically induced in 80 physically normal American men (varying ethnicity, average age 54). It was concluded: "Neither patient age nor size of the flaccid penis accurately predicted erectile length."

A study published in the December 2000 International Journal of Impotence Research found that average erect penis length in 50 Jewish Caucasian males was 13.6 cm (5.4 in) (measured by staff).[10] Quote: "The aim of this prospective study was to identify clinical and engineering parameters of the flaccid penis for prediction of penile size during erection." Erection was pharmacologically induced in 50 Jewish Caucasian patients who had been evaluated for erectile dysfunction (average age 47±14y). Patients with penis abnormalities or whose ED could be attributed to more than one psychological origin were omitted from the study.

A review published in the 2007 issue of BJU International showed the average erect penis length to be 14–16 cm (5.5–6.3 in) and girth to be 12–13 cm (4.7–5.1 in). The paper compared results of twelve studies conducted on different populations in several countries. Various methods of measurements were included in the review.[12]

An Italian study of about 3,300 men published in European Urology concluded that flaccid stretched length was measured on average to about 12.5 centimetres (4.9 in). In addition, they checked for correlations in a random subset of the sample consisting of 325 men. They found a few statistically significant Spearman's correlations: between flaccid length and height of 0.208, −0.140 with weight, and −0.238 with BMI, flaccid circumference and height 0.156, stretched length and height 0.221, weight −0.136, BMI −0.169. They also reported a few non-significant correlations.[17]

An Indian study of 500 men ages 18 to 60 published in the International Journal of Impotence Research found flaccid, stretched and erect length to be 8.21 cm, 10.88 cm and 13.01 cm, respectively.[14]

Erect circumference

Similar results exist regarding studies of the circumference of the adult fully erect penis, with the measurement taken mid-shaft.[citation needed] As with length, studies that relied on self-measurement consistently reported a significantly higher average than those with staff measuring. In a study of penis size where measurements were taken in a laboratory setting, the average penis circumference when erect was 4.8 inches (12.3 cm), which means that the average width of the erect penis is approximately 1.5 inches (4 cm).[18][19]

Size at birth

The average stretched penile length at birth is about 4 cm (1.6 in), and 90% of newborn boys will be between 2.4 and 5.5 cm (0.94 and 2.17 in). Limited growth of the penis occurs between birth and 5 years of age, but very little occurs between 5 years and the onset of puberty. The average size at the beginning of puberty is 6 cm (2.4 in) with adult size reached about 5 years later. W.A. Schonfeld published a penis growth curve in 1943.[20]

Size with aging

Authors of a paper reviewing research on area of penis sizes conclude that "flaccid penile length is just under 4 cm (1.6 in) at birth and changes very little until puberty, when there is marked growth."[2][12]

Age is not believed to negatively correlate with penis size. "Individual research studies have... suggested that penis size is smaller in studies focusing on older men, but Wylie and Eardley found no overall differences when they collated the results of various studies [over a 60 year period],"[12] however, there is some evidence to suggest that testicle size is getting progressively smaller with younger cohorts.[21]

Size and race

The belief that penis size varies according to race is not supported by scientific evidence.[12][22]

A 2007 study reported that contrary to the "popular belief that black people generally have longer penile sizes", in reality "there is no convincing scientific background" to support this idea.[23]

Variance

Micropenis

An adult penis with an erect length of less than 7 cm or 2.76 inches but otherwise formed normally is referred to in a medical context as having the micropenis condition.[24] The condition affects 0.6% of men.[13] Some of the identifiable causes are deficiency of pituitary growth hormone and/or gonadotropins, mild degrees of androgen insensitivity, a variety of genetic syndromes, and variations in certain homeobox genes. Some types of micropenis can be addressed with growth hormone or testosterone treatment in early childhood. Operations are also available to increase penis size in cases of micropenis in adults.[25]

Measuring erect micropenis

Environmental influence

It has been suggested that differences in penis size between individuals are caused not only by genetics, but also by environmental factors such as culture, diet, and chemical or pollution exposure.[26][27][28][29]Endocrine disruption resulting from chemical exposure has been linked to genital deformation in both sexes (among many other problems). Chemicals from both synthetic (e.g., pesticides, anti-bacterial triclosan, plasticizers for plastics) and natural (e.g., chemicals found in tea tree oil and lavender oil)[30][31] sources have been linked to various degrees of endocrine disruption. Both PCBs and the plasticizer DEHP have been associated with smaller penis size.[32] DEHP metabolites measured from the urine of pregnant women have been significantly associated with the decreased penis width, shorter anogenital distance, and the incomplete descent of testicles of their newborn sons, replicating effects identified in animals.[33] Approximately 25% of US women have phthalate levels similar to those in the study.[33] A 2007 study by University of Ankara, Faculty of Medicine found that penile size may decrease as a result of some hormonal therapy combined with external beam radiation therapy.[34] In addition, some estrogen-based fertility drugs like diethylstilbestrol (DES) have been linked to genital abnormalities and/or a smaller than normal penis (microphallus).[35]

World record claims

An American, Jonah Falcon, was reported in the early 2000s as having a 13.5-inch-long erect penis, claimed at the time to be the world's largest.[36][37]

Roberto Esquivel Cabrera is a Mexican man who, according to an X-ray conducted by the World Record Academy, has an 18.9-inch penis, surpassing Falcon's. He has said he wants to receive government benefits and be recognized as disabled because it prevents him from holding down a job, and also that women are too scared to have sex with him. Cabrera has expressed interest in having surgery to reduce the size of his penis. According to one doctor, most of his penis is in fact extra skin.[38]

Perceptions

Historical

According to Kenneth Dover's landmark study "Greek Homosexuality", Greek art had extreme interest in the genitals, but was not obsessed with size. The weekly Q&A column "The Straight Dope" deduces, based on pornographic Greek art work and Dover's aforementioned study, that in ancient Greece an uncircumcised and small penis was culturally seen as desirable in a man, whereas a bigger or circumcised penis was viewed as comical or grotesque, usually being found on "fertility gods, half-animal critters such as satyrs, ugly old men, and barbarians."[39]

CBC Radio has suggested, based on several sources, that ancient Romans had a viewpoint contrary to that of the Greeks.[5] This was also the case in medieval Arabic literature, where a longer penis was preferred, as described in an Arabian Nights tale called "Ali with the Large Member". As a witty satire of this fantasy, the 9th-century Afro-Arab author Al-Jahiz wrote: "If the length of the penis were a sign of honor, then the mule would belong to the Quraysh" (the tribe to which Muhammad belonged and from which he descended).[40]

18When she carried on her whoring so openly and flaunted her nakedness, I turned in disgust from her, as I had turned in disgust from her sister.19Yet she increased her whoring, remembering the days of her youth, when she played the whore in the land of Egypt20and lusted after her lovers there, whose members were like those of donkeys, and whose issue was like that of horses. Ezekiel 23:18–20, English Standard Version.

Male self-perception

Males may quite easily underestimate the size of their own penis relative to that of others, because of the foreshortening obtained from looking down, due to repeated observation of atypical penises in pornography, or because of the accumulation of fat at the base of the penis.[41] A survey by sexologists showed that many men who believed that their penis was of inadequate size had average-sized penises.[42] Another study found sex education of standard penile measurements to be helpful and relieving for patients concerned about small penis size, most of whom had incorrect beliefs of what is considered medically normal.[43] The perception of having a large penis is linked to higher self-esteem.[6]

Among gay men

A study undertaken at Utrecht University found that the majority of homosexual men in the study regarded a large penis as ideal, and having one was linked to self-esteem.[44] One study analysing the self-reported Kinsey data set found that the average penis of a homosexual man was larger than the average penis of their heterosexual counterparts (6.32 inches [16,05 cm] in length amongst gay men versus 5.99" [15,21 cm] in heterosexuals, and 4.95 inches [12,57 cm] circumference amongst gay men versus 4.80" [12,19 cm] in heterosexual men).[45][46]

Anxiety

Widespread private concerns related to penis size have led to a number of folklore sayings and popular culture reflections related to penis size. Penis panic is a form of mass hysteria involving the believed removal or shrinking of the penis, known as genital retraction syndrome. The penis can significantly shrink due to scar tissue formation from a condition called Peyronie's disease which affects up to 10% of men.[47] Products such as penis pumps, pills, and other dubious means of penis enlargement are some of the most marketed products in email spam. At present there is no consensus in the scientific community of any non-surgical technique that permanently increases either the thickness or length of the erect penis that already falls into the normal range (4.5" to 7").[48]

Size of other body parts

A statistically significant correlation between penis size and the size of other body parts has not been found in research. One study, Siminoski and Bain (1993), found a weak correlation between the size of the stretched penis and foot size and height; however, it was too weak to be used as a practical estimator.[49] Another investigation, Shah and Christopher (2002), which cited Siminoski and Bain (1993), failed to find any evidence for a link between shoe size and stretched penis size, stating "the supposed association of penile length and shoe size has no scientific basis".[50][51]

There may be a link between the malformation of the genitalia and the human limbs. The development of the penis in an embryo is controlled by some of the same Hox genes (in particular HOXA13 and HOXD13)[52] as those that control the development of the limbs. Mutations of some Hox genes that control the growth of limbs cause malformed genitalia (hand-foot-genital syndrome).[53]

Studies of size preferences among sexual partners

In a small study conducted by University of Texas–Pan American and published in BMC Women's Health, 50 undergraduate women were surveyed by two popular male athletes on campus about their perceptions of sexual satisfaction and it was concluded that the width of a penis feels better than the length of a penis, when subjects are asked to choose between the two (size was left unspecified). It was also concluded that this may show that penis size overall affects sexual satisfaction since women chose between the two options they were given.[54]

In a cover story by Psychology Today,[55][56] 1,500 readers (about two-thirds women) were surveyed about male body image. Many of the women were not particularly concerned with penis size and over 71% thought men overemphasized the importance of penis size and shape. Generally, the women polled cared more about width than men thought, and less about length than men thought, although the strength of caring for either among women showed a similar pattern.

Another study, conducted at Groningen University Hospital, asked 375 sexually active women (who had recently given birth) the importance of penis size the results of which showed that 21% of women felt length was important and 32% felt that girth was important.[57]

A study conducted at the Australian National University, published in early 2013, showed that penis size influences a man's sex appeal, and the taller the man, the bigger the effect.[58] The study showed 3D computer generated images at life size, altering the height and other physical attributes, with women typically registering preferences in under 3 seconds. A preference for taller men's larger penis size was notable.

A U.S. study published in 2015 of the stated preferences of a panel of 75 women using 3D-printed models as scale references showed a preferred penis length of 16 cm and a preferred circumference of 12.2 cm for long-term sexual partners, with slightly larger preferred sizes of a length of 16.3 cm and circumference of 12.7 cm for one-time sexual encounters.[59]

The term size queen is slang for anyone who prefers their sexual partner(s) to have a larger-than-average penis.[60]

Evolution

The human penis is thicker than that of any other primate, both in absolute terms and relative to the rest of the body.[61] Early research, based on inaccurate measurements, concluded that the human penis was also longer. In fact, the penis of the common chimpanzee is no shorter than in humans, averaging 14.4 cm (5.7 inches), and some other primates have comparable penis sizes relative to their body weight.[62]

The evolutionary reasons for the increased thickness have not been established.[63] One explanation is that thicker penises are an adaptation to a corresponding increase in vaginal size. The vaginal canal is believed to have expanded in humans to accommodate the larger size of a newborn's cranium. Women may then have sexually selected men with penises large enough to fit their vagina, to provide sexual stimulation and ensure ejaculation.[63]

Condom use

One Australian study of 184 men looked at penis length and circumference in relationship to condom breakage or slippage. 3,658 condoms were used. The study found that when used correctly condoms had a breakage rate of 1.34% and a slippage rate of 2.05%, for a total failure rate of 3.39%. Penile dimensions did not influence slippage, but penis circumference and broken condoms were strongly correlated, with larger sizes increasing the rate of breakage.[64]

^"A sample that is not representative of the population to which generalizations are to be made. For example, a group of band students would not be representative of all students at the middle school, and thus would constitute a biased sample if the intent was to generalize to all middle school students."Bureau of Justice Assistance website